Although significant advances in our knowledge of the moleular biology of hepatitis B virus (HBV) have been made, the mechanism of hepatocellular necrosis, the basic event in hepatitis B, remains unknown. The outer cell membrane probably represents the initial site of hepatocyte injury from immunologic reactions in hepatitis B. We postulate that the determinants, amount and structure of HBV antigens on the cell surface largely determine the interaction of infected hepatocytes with the host's immune response and that the expression of HBV antigens may be modulated by immune and non-immune factors. To understand the cellular and molecular basis of these interactions, we are studying 2 laboratory model systems of HBV infected cells: (1) human hepatocellular carcinoma cell lines (PLC/PRF/5 and Hep 3B) which resemble hepatocytes morphologically and functionally and are naturally infected with HBV; and (2) well defined subclones of NIH 3T3 mouse fibroblasts (4.10) which after transfection with cloned HBV DNA express all known HBV antigens (HBsAg, HBcAg, and HBeAg). Using poly- and monoclonal antibodies, fluorescence activated flow cytometry, quantitative radioimmunoassays and polypeptide analysis, we will define the HBV antigen(s) expressed, their amount, structure and relationship to host cell membrane proteins, particularly HLA class I and II antigens on the surface of cultured cells. Further, we will evaluate the effect of modulating agents, such as antibodies to HBV antigens and interferon-Gamma, on cell surface HBV antigens. Finally in a pilot study, we will explore the humoral and cellular immune response to HBV antigen positive subclones of 4.10 cells in NFS/N mice. These investigations may increase our understanding of the mechanism(s) whereby host immune factors lyse HBV-infected cells or modulate the expression of HBV antigens which may lead to virus persistence and chronic hepatitis B. This knowledge may result in a more rational approach to treatment of infected patients with interferon and prevention of hepatitis B by vaccination.